The present invention relates to a pivotable top board device for a chair and, more particularly, to a pivotable top board device for a chair for increasing stability during unfolding and folding operations.
Chairs used in conference rooms, classrooms, etc. generally include a top board that can be unfolded for easy writing for a user or can be folded when the user leaves the chair.
FIGS. 8 and 9 show a conventional chair with a pivotable top board device including an armrest 1′, an axle block 2′, a coupling board 3′, and a top board 4′. A receiving space 6′ is defined between the armrest 1′ and a body 5′ of the chair. The armrest 1′ includes a pivotal hole 11′. The axle block 2′ includes a first coupling face 21′ and a second coupling face 22′ at an angel of 45° to the first coupling face 21′. Each of the first and second coupling faces 21′ and 22′ has a stub 211′, 221′. The stub 211′ extends into the pivotal hole 11′ to be pivotably connected to the armrest 1′. A positioning groove 222′ is defined in the second coupling face 22′. The coupling board 3′ includes a side having a coupling face 31′ at an angel of 45° to a top face of the coupling board 3′. A pivotal hole 311′ is defined in the coupling face 31′ and pivotably receives the stub 221′ of the axle block 2′. A protrusion 312′ is provided on the coupling face 31′ in a location corresponding to the positioning groove 222′. The top board 4′ is fixed to the coupling board 3′. When not in use, the top board 4′ can be pivoted into the receiving space 6′. In use, the top board 4′ is lifted upward and pivots the axle block 2′ through an angle of 90° (see FIG. 10). Then, the top board 4′ is pivoted relative to the axle block 2′ to an extended position shown in FIG. 8, with the protrusion 312′ abutting against an edge of the positioning groove 222′.
However, stable operation of the coupling board 3′ and the axle block 2′ cannot be supported by the pivotal arrangement therebetween. For example, as shown in FIG. 11, the axle block 2′ is apt to pivot while the top board 4′ is being pivoted to the folded position, leading to deviation of the top board 4′ from the vertical direction. Thus, the angular position of the top board 4′ must be readjusted for the folding operation, which not only is inconvenient to folding but causes friction and wear between an edge of the top board 4′ and a surface of the armrest 1′.